Field of the Invention
The present invention relates to a metal mask and a screen printing apparatus.
Background Information
In recent years, in response to social demands and trends rooted in energy and environmental issues, fuel cells, which operate at normal temperature and from which high power density can be obtained, are gaining attention as sources of power for electric vehicles as well as stationary power sources. Because the product of the electrode reaction is primarily water, fuel cells can provide clean power generation systems with low impact on the global environment. Polymer electrolyte fuel cells (PEFC) in particular, due to their ability to operate at relatively low temperatures, are considered promising power sources for electric vehicles.
A polymer electrolyte fuel cell comprises an electrolyte membrane, a catalyst layer formed on both sides of the electrolyte membrane, and a membrane electrode assembly (Membrane Electrode Assembly, hereinafter referred to as MEA) that has a gas diffusion layer (GDL), etc. A fuel cell is configured by layering a plurality of MEAs with interposed separators.
The screen printing method is used in the manufacture of fuel cells and is a known technique in which an adhesive is applied in a rectangular shape, forming a gasket on the surface of the separator.
In the screen printing method, a separator as the object to be printed is disposed separated on the lower surface of a metal mask provided with openings, a gasket as a printing material is placed on the upper surface of the metal mask, and a squeegee is pressed and slid over the separator. Accordingly, the gasket is passed through the openings provided in the metal mask, and the gasket is applied onto the surface of the separator by transfer molding.
In a subsequent step, the separator, on the surface of which the gasket is applied, is pressurized and laminated with another separator so that the gaskets face each other. At this time, if there is a gap between the laminated gaskets, there is the risk that fuel gas or oxidant gas will leak through the gap to the outside. It is therefore necessary to form a closed rectangular pattern on the gasket that is applied to the surface of the separator.
In relation to the foregoing, for example, in Japanese Laid Open Patent Application No. 2007-331195, described below, a surface on one side of a bridge that is disposed between a pair of openings is aligned with a surface on the side over which the squeegee is slid, and the surface of the other side of the bridge is recessed from the back surface on the side that is opposite the side on which the squeegee is slid. The bridge is provided so at to connect the pair of openings. According to this metal mask, the gasket is filled in the recess provided on the other side surface of the bridge along with the openings by the sliding of the squeegee; therefore, it is possible to apply the gasket having a continuous closed pattern on the surface of the separator.